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Traditional red-light-emitting pyrotechnic formulations are based on strontium and chlorinated organic materials.[1] During their combustion, highly carcinogenic polychlorinated compounds are formed.[2] Additionally, strontium is classified as potentially harmful to human health by the United States Environmental Protection Agency.[3] Therefore, the goal of this project is to find a novel pyrotechnic system that will significantly reduce the environmental impact of pyrotechnics. These pyrotechnic systems are required to be free of chlorine (perchlorate), heavy metals and strontium and weight reduced. Furthermore, they should have high color purity and luminous intensity and no toxic solvents should be involved in synthesis and purification. To achieve these requirements, new lithium based pyrotechnical compositions with a high nitrogen content are tested. The lithium salt synthesis should be simple and easily scaled-up.
In the course of this project, more than 15 new lithium salts were synthesized and investigated. A considerable number of them were tested in pyrotechnic formulations. The opposing nature of spectral purity and light intensity resulted in the required parameters being attained, but not in a single formulation. Compared with a standard strontium formulation, the measured values of lithium flares at DEVCOM performed markedly inferior.
In the course of this project, more than 15 new lithium salts were synthesized and investigated. A considerable number of them were tested in pyrotechnic formulations. The opposing nature of spectral purity and light intensity resulted in the required parameters being attained, but not in a single formulation. Compared with a standard strontium formulation, the measured values of lithium flares at DEVCOM performed markedly inferior.
The reason for the poorer performance of the flares is the oxophilicity of lithium. This results in the formation of additional by-products, which have a negative influence on the coloration. Since the flares still contain additives (paper tubes), this can also influence the performance. High burning temperatures from the fuel can also be a negative influence.
1The Lithium Salts of Bis(azoyl)borates as Strontium- and Chlorine-free Red Pyrotechnic Colorants. Alicia M. W. Dufter, Thomas M. Klapötke, Magdalena Rusan, and Jörg Stierstorfer, Z. Anorg. Allg. Chem. 2020, 646, 580–585.
2Comparison of Functionalized Lithium Dihydrobis(azolyl)borates with Their Corresponding Azolates as Environmentally Friendly Red Pyrotechnic Coloring Agents. Alicia M. W. Dufter, Thomas M. Klapötke, Magdalena Rusan, Alexander Schweiger and Jörg Stierstorfer, ChemPlusChem. 2020, 85, 2044–2050.
3Lithium Nitropyrazolates as Potential Red Pyrotechnic Colorants. A. M. W. DufterMünster, Alexander G. Harter, Thomas M. Klapötke, Elena Reinhardt, Julia Römer and Jörg Stierstorfer, Eur. J. Inorg. Chem. 2022, in press.
4J. J. Sabatini, E.-C. Koch, J. C. Poret, J. D. Moretti, S. M. Harbol, Angew. Chem. 2015, 127, 11118–11120; Angew. Chem. Int. Ed. 2015, 54, 10968–10970.